Separation and purification method of polyarylene sulfide

ABSTRACT

The present disclosure relates to a method of more efficiently separating and purifying a polyarylene sulfide exhibiting excellent strength, heat resistance, flame retardancy, and processability when processed into a molded product after polymerization.

The present application is a National Phase entry pursuant to 35 U.S.C.§ 371 of International Application No. PCT/KR2019/013771 filed on Oct.18, 2019, and claims priority to and the benefit of Korean PatentApplications No. 10-2018-0125505 filed on Oct. 19, 2018 and No.10-2019-0129387 filed on Oct. 17, 2019 with the Korean IntellectualProperty Office, the disclosures of which are incorporated herein byreference in their entirety.

FIELD

The present disclosure relates to a method of more efficientlyseparating and purifying a polyarylene sulfide exhibiting excellentstrength, heat resistance, flame retardancy, and processability whenprocessed into a molded product after polymerization.

BACKGROUND

Polyarylene sulfide (PAS), which is represented by polyphenylene sulfide(PPS), has been widely used in automobiles, electrical and electronicproducts, machinery and the like to replace metals, especially diecasting metals such as aluminum and zinc, due to its excellent strength,heat resistance, flame retardancy, and processability. Particularly,since the PPS resin has excellent flowability, it is suitable to use itas a compound by kneading with a filler such as glass fiber or areinforcing agent.

Generally, PAS is prepared by polymerizing a sulfur source and adihalogenated aromatic compound in the presence of an amide-basedcompound such as N-methyl pyrrolidone (NMP). Since the polymerizationreaction of this method is a desalination polycondensation mechanism, alarge amount of by-products such as sodium chloride are produced.Therefore, a process of removing the by-products is necessary after thepolymerization reaction. However, it is difficult to completely removethe by-products in ordinary treatment, and commercially availablegeneral-purpose PPS products contain about thousands ppm of alkalimetals. When alkali metal salts remain in the resulting polymer,deterioration of physical properties such as electrical properties mayoccur. Therefore, when a molded product prepared by using this PAS as araw material is applied to electrical and electronic components,deterioration of electrical properties by the alkali metal in PAS is abig obstacle.

Accordingly, various methods are currently known for removingby-products such as sodium chloride from the PAS component. For example,Japanese Patent Publication No. 1986-220446 discloses a method ofrepeatedly washing a reaction product containing PPS with water and hotwater, and then washing with an acidic aqueous solution, followed bywashing with ion-exchanged water, wherein the PPS is obtained byreacting sodium hydrosulfide, sodium hydroxide and p-dichlorobenzene inN-methyl-2-pyrrolidone. Specifically, in order to remove the metalcompound (by-product) generated in the PAS manufacturing process, amixture containing solid PAS and a metal compound is contacted withwater and the metal compound is dissolved in water and removed from thePAS. However, this method requires a long washing time using a largeamount of water to remove metal impurities, and thus a very large andcomplicated process is required. In addition, there is a problem in thatit is also necessary to treat a large amount of aqueous wastewatergenerated in the washing process. Process costs and the emission ofenvironmental pollutants are high. Recently, a method of removingby-products such as sodium chloride from the PAS component has beenknown, in which the PAS component is separated by filtration using avibrating mesh and sodium chloride is passed together with wasteslurries. However, in this case, mesh holes are blocked by the sodiumchloride fine powders, thereby reducing separation efficiency afterseveral filtration processes.

In addition, even after PAS is polymerized, remaining unreactedsubstance is removed by washing with an organic solvent such asN-methyl-2-pyrrolidone (NMP) and acetone, or water. The organic solventsuch as N-methyl-2-pyrrolidone as described above is not only expensivebut also known to be a major cause of environmental pollution whendischarged in the form of an aqueous solution. Therefore, it isgenerally recovered, purified and reused. However, since the organicsolvent such as N-methyl-2-pyrrolidone has high solubility in organics,it has excellent compatibility with water and it is mixed with waterinfinitely. In addition, when a large amount of an inorganic salt isdissolved such as an effluent from a PAS manufacturing process, it isdifficult to distill as-is, so various separation and purificationmethods have been tried. However, when water-washing is performed toremove by-products such as sodium chloride from the PAS component, theorganic solvent used to wash the PAS is mixed with water, making itexpensive to recover the organic solvent.

Accordingly, there is a continuing demand for development of a processfor more efficiently separating and purifying a polyarylene sulfidewithout reducing separation efficiency, even if applied several times insuccession, while increasing a recovery rate of the organic solvent withminimal energy consumption and washing costs of the entire process.

SUMMARY

The present disclosure provides a method of more efficiently separatingand purifying polyarylene sulfide exhibiting excellent strength, heatresistance, flame retardancy, and processability when processed into amolded product after polymerization.

The present disclosure is also to provide a preparation method of apolyarylene sulfide including the separation and purification process asdescribed above.

According to one embodiment of the present disclosure, there is provideda separation and purification method of a polyarylene sulfide, includingthe steps of: separating polyarylene sulfide particles by sedimentation,and then removing alkali metal halide particles with an organic solventby sedimentation from a mixed solution containing polyarylene sulfideparticles, alkali metal halide particles and an organic solvent using adecanter centrifugal separator at 1000 rpm to 2500 rpm; and drying theseparated polyarylene sulfide particles at 100° C. to 200° C. beforewashing with water.

According to another embodiment of the present disclosure, there isprovided a preparation method of a polyarylene sulfide, including thesteps of: preparing a sulfur source including a sulfide of an alkalimetal and a mixed solvent of water and an amide-based compound bydehydrating a hydrosulfide of an alkali metal and a hydroxide of analkali metal in a mixed solvent of water and the amide-based compound;preparing polyarylene sulfide particles together with alkali metalhalide particles by adding a dihalogenated aromatic compound and anamide-based compound to a reactor containing the sulfur source, andperforming a polymerization reaction; washing the polymerization productcontaining the polyarylene sulfide particles and the alkali metal halideparticles with an organic solvent; separating the polyarylene sulfideparticles by sedimentation, and then removing the alkali metal halideparticles with the organic solvent by sedimentation from a mixedsolution containing the polyarylene sulfide particles, the alkali metalhalide particles and the organic solvent by using a decanter centrifugalseparator at 1000 rpm to 2500 rpm; and drying the separated polyarylenesulfide particles at 100° C. to 200° C. before washing with water.

As described above, in the present disclosure, polyarylene sulfideparticles may be first separated by sedimentation depending on thedifference in particle size without degrading separation efficiency dueto the alkali metal halide particles, and then dried under optimumconditions to perform water-washing with no organic solvent remaining,thereby increasing a recovery rate of the organic solvent andsignificantly reducing recovery costs. Therefore, the present disclosuremay efficiently separate and purify polyarylene sulfide particles withhigh separation efficiency even if separated several times insuccession.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a process for separating and purifying apolyarylene sulfide in Example 1 according to one embodiment of thepresent disclosure.

FIG. 2 is a schematic view illustrating a process of removal of alkalimetal halide particles by sedimentation after separating polyarylenesulfide particles by sedimentation in a decanter centrifugal separatoraccording to Example 1.

FIG. 3 is a schematic view of a process for separating and purifying apolyarylene sulfide in Comparative Example 1 according to the prior art.

FIG. 4 is a schematic view illustrating a process of filteringpolyarylene sulfide particles in a vibrating mesh to separate and purifythem on the upper part, followed by removing alkali metal halideparticles by passing them downward according to Comparative Example 1.

DETAILED DESCRIPTION

In the present disclosure, the terms “the first”, “the second”, and thelike are used to describe a variety of components, and these terms aremerely employed to distinguish a certain component from othercomponents.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.The singular forms are intended to include the plural forms as well,unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “include”, “have”, or “possess” when used inthis specification, specify the presence of stated features, numbers,steps, components, or combinations thereof, but do not preclude thepresence or addition of one or more other features, numbers, steps,components, or combinations thereof.

As the present invention can be modified and have various forms,specific embodiments thereof are shown by way of examples and will bedescribed in detail. However, it is not intended to limit the presentinvention to the particular form disclosed and it should be understoodthat the present invention includes all modifications, equivalents, andreplacements within the idea and technical scope of the presentinvention.

Hereinafter, the present disclosure will be described in detail.

The present disclosure provides a method for efficiently separating andpurifying polyarylene sulfide particles from a mixed solution containingpolyarylene sulfide particles, alkali metal halide particles and anorganic solvent.

In particular, the present disclosure is to efficiently separatepolyarylene sulfide particles from a waste liquid obtained after washingthe polyarylene sulfide particles produced in a polyarylene sulfide(PAS) manufacturing process with an organic solvent. Specifically, thepolyarylene sulfide particles are first separated by sedimentationdepending on the difference in particle size using a decantercentrifugal separator, and then dried under optimum conditions toperform water-washing with no organic solvent remaining, therebyincreasing a recovery rate of the organic solvent and significantlyreducing recovery costs.

In addition, in the present disclosure, the polyarylene sulfideparticles produced after polymerization are first separated bysedimentation depending on the difference in particle size using adecanter centrifugal separator, thereby removing the organic solvent andalkali metal halide particles with the waste liquid by sedimentation.Therefore, the present disclosure may efficiently separate and recoverpolyarylene sulfide particles without degrading separation efficiencyeven if separated several times in succession.

According to one embodiment of the present disclosure, the separationand purification method of a polyarylene sulfide separates polyarylenesulfide particles and an organic solvent using a decanter centrifugalseparator from a mixed solution containing polyarylene sulfideparticles, alkali metal halide particles and an organic solvent, andthen removes the organic solvent by an optimized drying process beforewashing with water.

Specifically, the separation and purification method of a polyarylenesulfide includes a step of separating polyarylene sulfide particles withan organic solvent by sedimentation, and then removing alkali metalhalide particles by sedimentation from a mixed solution containingpolyarylene sulfide particles, alkali metal halide particles and anorganic solvent using a decanter centrifugal separator at 1000 rpm to2500 rpm.

In the separation and purification method of a polyarylene sulfide, adecanter centrifugal separator is used instead of a conventionalvibrating mesh, so that a problem of poor separation efficiency due toblocked mesh holes can be solved. That is, when the polyarylene sulfideparticles are separated and purified by filtration, the mesh holes areblocked by the alkali metal halide particles after several filtrationprocesses, thereby reducing the separation efficiency. However, thepresent disclosure is characterized in that the separation efficiencydoes not decrease even if separated several times in succession.

In particular, the present disclosure uses the decanter centrifugalseparator at 1000 rpm to 2500 rpm, and does not perform separation bysedimentation depending on the difference in specific gravity ofparticles which is commonly known. Specifically, the present disclosureis characterized in that, despite a high specific gravity of alkalimetal halide particles such as sodium chloride, polyarylene sulfideparticles are first separated and purified by the difference insedimentation velocity depending on the difference in particle size.

The decanter centrifugal separator may be used at 1000 rpm to 2500 rpmto make a difference in sedimentation velocity depending on thedifference in particle size. When the decanter centrifugal separator isused at higher than 2500 rpm, the sedimentation of alkali metal halidesis accelerated, resulting in coming out with polyarylene sulfide (PAS),and thereby lowering the separation efficiency. When the decantercentrifugal separator is used at lower than 1000 rpm, the sedimentationtakes a long time, thereby increasing an amount of waste liquid in thepolyarylene sulfide (PAS).

At this time, the decanter centrifugal separator may be used at atemperature of room temperature to 180° C., and a pressure of normalpressure to 5 bar. Herein, the room temperature refers to an ambienttemperature at normal pressure, and may be about 20° C. to about 28° C.,or about 22° C. to about 26° C. In addition, the normal pressure refersto an atmospheric pressure without a separate reduced pressure orpressurized condition, and may be about 0.95 atm to about 1.1 atm, orabout 0.95 bar to about 1.1 bar.

The specific kind of the decanter centrifugal separator that can be usedin the separation and purification process of a polyarylene sulfideaccording to the present disclosure is not particularly limited. Forexample, the decanter centrifugal separator is generally commerciallyavailable, and a commercially available one can be used in the presentdisclosure.

The decanter centrifugal separator is a device capable of separating aliquid-liquid mixture or a liquid-solid mixture by sedimentation,dehydration, concentration, etc. using centrifugal force. Generally, thedecanter centrifugal separator is known to sediment and separateparticles having a large specific gravity depending on the difference inspecific gravity, that is, density of particles. However, the presentdisclosure is characterized in that the decanter centrifugal separatoris operated under optimum conditions to separate polyarylene sulfideparticles first by sedimentation and then remove alkali metal halideparticles by sedimentation depending on the difference in particle size,not depending on the difference in specific gravity.

The present disclosure is to efficiently separate polyarylene sulfideparticles from a waste liquid containing polyarylene sulfide particlesproduced in a polyarylene sulfide (PAS) manufacturing process, variousinorganic salts and impurities. Accordingly, the mixed solutionintroduced into the decanter centrifugal separator may be a waste liquidor a mixed liquid thereof produced in a synthesizing or washing processof a polyarylene sulfide, and may further contain at least one selectedfrom the group consisting of sodium hydroxide (NaOH), sodium acetate(NaOAc), sodium sulfide (Na₂S), sodium hydrosulfide (NaSH), andp-dichlorobenzene in addition to polyarylene sulfide particles which areproducts of the polymerization process, alkali metal halide particleswhich are by-products, and an organic solvent and water which are usedfor washing.

Herein, specific examples of the polyarylene sulfide particles includepolyphenylene sulfide (PPS).

The polyarylene sulfide particles may have a particle size of 100micrometers (μm) to 2000 micrometers (μm), or 150 μm to 1800 μm.

For example, the particle size of polyarylene sulfide may be measuredusing standard mesh sieve having various sieve sizes such as 100 μm, 40μm, or 10 μm.

Specific conditions for measuring the particle size of polyarylenesulfide are not particularly limited. For example, the particle size maybe measured after the polyarylene sulfide particles are stored at about22° C. to 26° C. under a relative humidity of 60% to 78% for at leastabout 3 hours, preferably at least about 6 hours, at least about 9hours, at least about 15 hours, or at least about 24 hours.

In addition, the polyarylene sulfide particles may have a density of 1g/cm³ to 1.5 g/cm³, or 1.1 g/cm³ to 1.45 g/cm³.

For example, the density may be measured by the method of the AmericanSociety for Testing and Materials, ASTM D 1505.

Meanwhile, specific examples of the alkali metal halide particlesproduced as a by-product together with the polyarylene sulfide particlesin the polyarylene sulfide (PAS) manufacturing process include sodiumchloride (NaCl), sodium iodide (NaI), and the like, and any one or amixture of two or more thereof may be used.

The alkali metal halide particles may have a particle size of 5 μm to 30μm, or 6 μm to 28 μm.

In addition, the alkali metal halide particles may have a density of 1.9g/cm³ to 3 g/cm³, or 2 g/cm³ to 2.8 g/cm³.

Herein, the size and density of the alkali metal halide particles may bemeasured in the same manner as the polyarylene sulfide particles.

In addition, the organic solvent contained with the polyarylene sulfideparticles produced in the polyarylene sulfide (PAS) manufacturingprocess and the alkali metal halide particles which are by-products isused in the washing process, and may be at least one selected from thegroup consisting of N-methyl-2-pyrrolidone (NMP), acetone, and isopropylalcohol (IPA).

According to one embodiment of the present disclosure, after separatingthe polyarylene sulfide particles and the organic solvent using adecanter centrifugal separator as described above, a step of removingthe organic solvent, etc. is performed by a first drying process beforewashing the separated polyarylene sulfide particles with water.

In particular, the first drying process before washing the polyarylenesulfide particles is performed at about 100° C. to about 200° C. priorto water-washing, so that the water-washing can be performed with noorganic solvent remaining, thereby increasing a recovery rate of theorganic solvent and reducing recovery costs.

The first drying process may be performed at about 100° C. to about 200°C., preferably at about 120° C. to about 190° C., or at about 135° C. toabout 180° C. In particular, the first drying process may be performedat about 100° C. or more, preferably at about 120° C. or more, or atabout 135° C. or more to evaporate the organic solvent used forpolymerization or washing. In addition, the first drying process may beperformed at about 200° C. or less, preferably at about 190° C. or less,or at about 180° C. or less, in order to prevent cross-linking of thepolyarylene sulfide (PAS) caused by contact with hot air.

In addition, the first drying process may be performed under normalpressure or reduced pressure. The normal pressure is as described above,and the reduced pressure refers to a pressure below the normal pressure.For example, the first drying process may be performed under a pressureof 4×10⁻¹⁴ bar to 1.1 bar, 4×10⁻¹° bar to 1.1 bar, or 4×10⁻⁶ bar to 1.1bar. In particular, it may be performed under reduced pressure in orderto facilitate the evaporation of the organic solvent and to preventcross-linking.

In the present disclosure, water-washing with no organic solventremaining can be performed by the above first drying process beforewashing the polyarylene sulfide particles, and the polyarylene sulfideparticles obtained after the drying process may have a residual amountof the organic solvent of 0.5 wt % or less, 0.3 wt % or less, or 0.1 wt% or less.

Subsequently, after removing the organic solvent, etc. by the firstdrying process, water-washing of the polyarylene sulfide particles maybe further performed once or twice or more. In addition, after washingthe dried polyarylene sulfide particles with water, a second dryingprocess may be further performed to remove a solvent such as water. Thesecond drying process may be performed at about 100° C. to about 200°C., preferably at about 130° C. to about 190° C., or at about 140° C. toabout 180° C. In particular, the second drying process may be performedat about 100° C. or more, preferably at about 130° C. or more, or atabout 140° C. or more to evaporate the solvent such as water after thewashing process. In addition, the second drying process may be performedat about 200° C. or less, preferably at about 190° C. or less, or atabout 180° C. or less, in order to prevent cross-linking of thepolyarylene sulfide (PAS) caused by contact with hot air.

In addition, the second drying process may be performed under normalpressure or reduced pressure. The normal pressure is as described above,and the reduced pressure refers to a pressure below the normal pressure.For example, the second drying process may be performed under a pressureof 4×10⁻¹⁴ bar to 1.1 bar, 4×10⁻¹⁰ bar to 1.1 bar, or 4×10⁻⁶ bar to 1.1bar. In particular, it may be performed under reduced pressure in orderto facilitate the evaporation of the solvent such as water and toprevent cross-linking.

In the separation and purification method of a polyarylene sulfide asdescribed above, polyarylene sulfide particles are first separated bysedimentation depending on the difference in particle size using adecanter centrifugal separator, and then dried under optimum conditionsto perform water-washing with no organic solvent remaining, therebyincreasing a recovery rate of the organic solvent and significantlyreducing recovery costs.

In particular, a recovery yield of polyarylene sulfide (PAS) particlesseparated and purified through the separation and purification processof the present disclosure may be about 90% or more, about 95% or more,or about 98% or more. And a residual amount of the organic solvent inwashing water obtained from the water-washing process may be about 0.5wt % or less, about 0.1 wt % or less, or 0.05 wt % or less.

Meanwhile, according to another embodiment of the present disclosure,there is provided a preparation method of a polyarylene sulfideincluding the separation and purification process as described above.

The preparation method of a polyarylene sulfide includes the steps of:preparing a sulfur source including a sulfide of an alkali metal and amixed solvent of water and an amide-based compound by dehydrating ahydrosulfide of an alkali metal and a hydroxide of an alkali metal in amixed solvent of water and an amide-based compound (first step);preparing polyarylene sulfide particles together with alkali metalhalide particles by adding a dihalogenated aromatic compound and anamide-based compound to a reactor containing the sulfur source, andperforming a polymerization reaction (second step); washing thepolymerization product containing the polyarylene sulfide particles andthe alkali metal halide particles with an organic solvent (third step);separating the polyarylene sulfide particles by sedimentation, and thenremoving the alkali metal halide particles with the organic solvent bysedimentation from a mixed solution containing the polyarylene sulfideparticles, the alkali metal halide particles and the organic solventusing a decanter centrifugal separator at 1000 rpm to 2500 rpm (fourthstep); and drying the separated polyarylene sulfide particles at 100° C.to 200° C. before washing with water (fifth step).

The preparation method of a polyarylene sulfide according to anotherembodiment of the present disclosure will be described in each step.

The above-described first step is preparing a sulfur source.

The sulfur source is prepared by dehydrating a hydrosulfide of an alkalimetal, and a hydroxide of an alkali metal in a mixed solvent of waterand an amide-based compound. Therefore, the sulfur source may includethe mixed solvent of water and an amide-based compound remaining afterthe dehydration, together with a sulfide of an alkali metal prepared bythe reaction of the hydrosulfide of an alkali metal with the hydroxideof an alkali metal.

Meanwhile, the sulfide of an alkali metal may be determined depending onthe type of the hydrosulfide of an alkali metal used in the reaction.Specific examples thereof include lithium sulfide, sodium sulfide,potassium sulfide, rubidium sulfide, and cesium sulfide, and any one ora mixture of two or more thereof may be used.

Specific examples of the hydrosulfide of an alkali metal that can beused in the preparation of the sulfur source by reacting thehydrosulfide of an alkali metal with the hydroxide of an alkali metalinclude lithium hydrogen sulfide, sodium hydrosulfide, potassiumhydrogen sulfide, rubidium hydrogen sulfide, cesium hydrogen sulfide,and the like. Any one or a mixture of two or more thereof may be used,and an anhydride or a hydrate thereof may be used.

Specific examples of the hydroxide of an alkali metal include lithiumhydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide,cesium hydroxide and the like, and any one or a mixture of two or morethereof may be used. The hydroxide of an alkali metal may be used in anamount of 0.90 to 2.0 equivalents, more specifically 1.0 to 1.5equivalents, and more particularly 1.0 to 1.2 equivalents, based on 1equivalent of the hydrosulfide of an alkali metal.

In the present disclosure, the equivalent refers to molar equivalent(eq/mol).

Further, in the preparation of the sulfur source by the reaction of thehydrosulfide of an alkali metal with the hydroxide of an alkali metal,an organic acid salt of an alkali metal capable of promoting thepolymerization reaction and raising the degree of polymerization of apolyarylene sulfide in a short period of time may be added as apolymerization assistant. Specific examples of the organic acid salt ofan alkali metal include lithium acetate, sodium acetate, and the like,and any one or a mixture of two or more thereof may be used. The organicacid salt of an alkali metal may be used in an amount of about 0.01 to1.0 equivalent, specifically about 0.01 to 0.8 equivalent, and morespecifically about 0.05 to 0.5 equivalents, based on 1 equivalent of thehydrosulfide of an alkali metal.

The reaction between the hydrosulfide of an alkali metal and thehydroxide of an alkali metal may be carried out in a mixed solvent ofwater and an amide-based compound. Specific examples of the amide-basedcompound include amide compounds such as N,N-dimethylformamide orN,N-dimethylacetamide, pyrrolidone compounds such asN-methyl-2-pyrrolidone (NMP) or N-cyclohexyl-2-pyrrolidone; caprolactamcompounds such as N-methyl-ε-caprolactam, imidazolidinone compounds suchas 1,3-dialkyl-2-imidazolidinone, urea compounds such as tetramethylurea; phosphoric acid amide compounds such as hexamethylphosphoric acidtriamide; and the like, and any one or a mixture of two or more thereofmay be used. Among them, the amide-based compound may preferably beN-methyl-2-pyrrolidone (NMP), considering a reaction efficiency and acosolvent effect as a polymerization solvent for preparing a polyarylenesulfide.

The water may be used in an amount of about 1 to 8 equivalents,specifically about 1.5 to 5 equivalents, and more specifically about 2.5to 5 equivalents, based on 1 equivalent of the amide-based compound.

Meanwhile, in the first step, a sulfide of an alkali metal may beprepared by dehydrating reactants containing a hydrosulfide of an alkalimetal, a hydroxide of an alkali metal and the like. Herein, thedehydration reaction may be performed by stirring at about 100 rpm to500 rpm at a temperature of about 130° C. to 205° C. More specifically,the dehydration reaction may be performed by stirring at about 100 rpmto 300 rpm at a temperature of about 175° C. to 200° C. The dehydrationreaction may be performed for about 30 minutes to 6 hours, or for about1 hour to 3 hours.

During the dehydration reaction, the solvent such as water in thereactants may be removed by distillation or the like, and some of theamide-based compound may be discharged together with the water. Inaddition, some of the sulfur contained in the sulfur source may reactwith water by heat during the dehydration reaction, and may bevolatilized as hydrogen sulfide gas.

As a result of the reaction of the hydrosulfide of an alkali metal, thehydroxide of an alkali metal and the alkali metal salt, a sulfide of analkali metal is precipitated in a solid phase in a mixed solvent ofwater and an amide-based compound. Accordingly, when the sulfur sourceprepared by reacting the hydrosulfide of an alkali metal with thehydroxide of an alkali metal is used as a sulfur source in thepreparation of a polyarylene sulfide according to the presentdisclosure, the molar ratio of the sulfur source refers to a molar ratioof the hydrosulfide of an alkali metal added during the reaction.

Subsequently, in order to remove the solvent such as water from thereaction product containing the sulfide of an alkali metal produced as aresult of the above reaction, a dehydration process is performed. Thedehydration process may be carried out according to a method well knownin the art. The conditions are not particularly limited, and thespecific process conditions are as described above.

Further, during the dehydration reaction, the sulfur contained in thesulfur source reacts with water to produce hydrogen sulfide and ahydroxide of an alkali metal, and the generated hydrogen sulfide isvolatilized. Therefore, the amount of sulfur in the sulfur sourceremaining in the system after the dehydration reaction may be reduced bythe hydrogen sulfide which is volatilized out of the system during thedehydration reaction. For example, when using the sulfur source mainlycontaining a hydrosulfide of an alkali metal, the amount of sulfurremaining in the system after the dehydration reaction is equal to themolar amount of sulfur in the introduced sulfur source minus the molaramount of hydrogen sulfide volatilized out of the system. Therefore, itis necessary to quantify the amount of effective sulfur contained in thesulfur source remaining in the system after the dehydration reactionfrom the amount of hydrogen sulfide volatilized out of the system.Specifically, the dehydration reaction is performed until the molarratio of water to 1 mol of effective sulfur is 1 to 5, specifically 1.5to 4, more specifically 1.75 to 3.5. When the water content in thesulfur source is excessively decreased by the dehydration reaction,water may be added to adjust the water content before the polymerizationprocess.

Accordingly, the sulfur source prepared by the reaction of thehydrosulfide of an alkali metal with the hydroxide of an alkali metaland the dehydration as described above may include a mixed solvent ofwater and an amide-based compound together with a sulfide of an alkalimetal, and the water may be included in a molar ratio of 1.75 to 3.5based on 1 mol of sulfur contained in the sulfur source. In addition,the sulfur source may further include a hydroxide of an alkali metalprepared by the reaction of sulfur with water.

According to one embodiment of the present disclosure, the second stepis polymerizing the sulfur source with a dihalogenated aromatic compoundto prepare a polyarylene sulfide.

The dihalogenated aromatic compound usable for the preparation of thepolyarylene sulfide is a compound in which two hydrogen atoms of anaromatic ring are substituted with halogen atoms. Specific examplesthereof include o-dihalobenzene, m-dihalobenzene, p-dihalobenzene,dihalotoluene, dihalonaphthalene, dihalobiphenyl, dihalobenzoic acid,dihalodiphenyl ether, dihalodiphenylsulfone, dihalodiphenylsulfoxide,and dihalodiphenylketone, and any one or a mixture of two or morethereof may be used. In the dihalogenated aromatic compound, the halogenatom may be fluorine, chlorine, bromine or iodine. Among them,p-dichlorobenzene (p-DCB) may preferably be used in order to increasereactivity and suppress side reactions in the preparation of apolyarylene sulfide.

The dihalogenated aromatic compound may be added in an amount of about0.8 to 1.2 equivalents based on 1 equivalent of the sulfur source. Whenthe dihalogenated aromatic compound is added within the above range, apolyarylene sulfide having excellent physical properties may be obtainedwithout lowering melting viscosity of the prepared polyarylene sulfideand increasing the content of chlorine present in the polyarylenesulfide. Considering the excellent effect of controlling the additionamount of the sulfur source and the dihalogenated aromatic compound, thedihalogenated aromatic compound may be added in an amount of about 0.9to 1.1 equivalents.

Further, a step of lowering the temperature of the reactor containingthe sulfur source to a temperature of about 150° C. to 200° C. may befurther included before the second step to prevent vaporization of thedihalogenated aromatic compound.

Further, the polymerization reaction of the sulfur source and thedihalogenated aromatic compound may be carried out in a solvent of anamide-based compound which is a polar aprotic organic solvent and stableto an alkali at a high temperature.

Specific examples of the amide-based compound are as described above,and pyrrolidone compounds such as N-methyl-2-pyrrolidone (NMP) orN-cyclohexyl-2-pyrrolidone are preferable considering the reactionefficiency.

Since the amide-based compound contained in the sulfur source in thefirst step functions as a co-solvent, the amide-based compound may beadded in the second step in a molar ratio of water (H₂O) to theamide-based compound present in the polymerization system (a ratio ofwater/an amide-based compound) to be about 0.85 or more.

During the polymerization reaction, other additives such as a molecularweight regulator, a cross-linking agent and the like for controlling thepolymerization reaction or the molecular weight may be further added inan amount not lowering physical properties and the yield of thepolyarylene sulfide to be finally prepared.

The polymerization reaction of the sulfur source and the dihalogenatedaromatic compound may be performed at about 200° C. to 300° C.Alternatively, the polymerization reaction may be performed in multiplesteps, varying the temperature within the above-mentioned temperaturerange. Specifically, after the first polymerization reaction at about200° C. or more and less than 250° C., the second polymerizationreaction may be performed at a temperature higher than that of the firstpolymerization reaction, specifically at about 250° C. to 300° C.

The polyarylene sulfide produced as a result of the polymerizationreaction is in the form of particles, and alkali metal halide particlesare produced as a by-product together with the polyarylene sulfideparticles.

The features related to the polyarylene sulfide particles and the alkalimetal halide particles thus produced are as described above, and adetailed description thereof will be omitted.

According to one embodiment of the present disclosure, the third step iswashing the reaction product produced as a result of the polymerizationreaction with an organic solvent in order to remove impurities such asoligomers.

Specific examples of the organic solvent include N-methyl-2-pyrrolidone(NMP), acetone, isopropyl alcohol (IPA), and the like, and any one or amixture of two or more thereof may be used.

This washing process with an organic solvent may be carried outaccording to a method well known in the art, and the conditions are notparticularly limited.

According to one embodiment of the present disclosure, the fourth stepis separating and purifying the polyarylene sulfide particles bysedimentation from the reaction product produced as a result of thepolymerization reaction.

For separating and purifying the polyarylene sulfide particles, a mixedsolution containing polyarylene sulfide particles, alkali metal halideparticles and an amide-based compound is introduced into a decantercentrifugal separator, and the decanter centrifugal separator isoperated at 1000 rpm to 2500 rpm to separate the polyarylene sulfideparticles by sedimentation first, followed by sedimentation and removalof the alkali metal halide particles.

In another embodiment of the present disclosure, the features related tothe sedimentation and separation process of polyarylene sulfideparticles using a decanter centrifugal separator are as described above,and a detailed description thereof will be omitted.

According to one embodiment of the present disclosure, the fifth step isremoving the organic solvent, etc. by the first drying process beforewashing the separated polyarylene sulfide particles with water, afterthe polyarylene sulfide particles and the organic solvent are separatedusing a decanter centrifugal separator as described above.

In particular, the first drying process before washing the polyarylenesulfide particles is performed at about 100° C. to about 200° C. priorto water-washing, so that the water-washing can be performed with noorganic solvent remaining, thereby increasing a recovery rate of theorganic solvent and reducing recovery costs.

In another embodiment of the present disclosure, the features related tothe first drying process of polyarylene sulfide particles before washingwith water are as described above, and a detailed description thereofwill be omitted.

Thereafter, the separated and purified polyarylene sulfide particles maybe optionally further washed with water, etc., filtered or driedaccording to a conventional method.

As a specific preparation method of the polyarylene sulfide, followingexamples may be referred to. However, the preparation method of thepolyarylene sulfide is not limited to this description. The preparationmethod may further include a step which is usually carried out in thetechnical field of the present invention, and the step(s) of thepreparation method may be changed by the step(s) usually changeable.

Hereinafter, the present invention will be described in more detail withreference to the following preferred examples. However, these examplesare for illustrative purposes only, and the invention is not intended tobe limited by these examples.

EXAMPLES Example 1

1-1. Preparation of Polyphenylene Sulfide

Sodium sulfide was prepared by mixing 70% sodium hydrosulfide (NaSH) andsodium hydroxide (NaOH) in an equivalent ratio of 1:1.05 to prepare aPPS polymer. At this time, 0.4 equivalent of sodium acetate (CH₃COONa)powder, 1.65 equivalents of N-methyl-2-pyrrolidone (NMP), and 4.72equivalents of deionized water (DI water) were added to the reactor.Herein, the equivalent refers to molar equivalent (eq/mol). At thistime, the solid reagent was added first, followed by NMP, DI water.Then, the reactor was stirred at about 150 rpm and heated to about 195°C. for 1 hour and 40 minutes to dehydrate. Thereafter, the temperatureof the reactor was lowered to about 175° C., and 1.02 times moreequivalent of para-dichlorobenzene (p-DCB) than sodium hydrosulfide and1.35 equivalents of N-methyl-2-pyrrolidone (NMP) were added to thereactor. Thereafter, the reaction mixture was heated to about 230° C.and reacted for about 2 hours as a front reaction, and further heated toabout 255° C. and reacted for about 2 hours as a rear reaction, followedby addition of 3 equivalents of distilled water and stirring for about 5minutes. As a result, 500 g of a slurry containing PPS polymer particleswas obtained. The slurry contained polyarylene sulfide particles, alkalimetal halide particles, and an amide-based compound.

1-2. Separation and Purification of Polyphenylene Sulfide

100 g of the slurry produced in step 1-1 was aliquoted and washed onceusing 100 g of NMP. The obtained mixed solution was subjected tofiltration using a decanter centrifugal separator to separate apolyarylene sulfide as a PPS wet cake as shown in FIG. 1. At this time,the decanter centrifugal separator was operated at 1000 rpm under roomtemperature and normal pressure conditions.

The PPS wet cake thus obtained was subjected to a first vacuum dryingprocess under a pressure of about 0.15 bar or less at a temperature of150° C. prior to washing with water to make a dry PPS. A residual amountof the organic solvent in the dry PPS was 0.5 wt % or less. Thereafter,washing was repeated four times using 50 g of water, and then a secondvacuum drying process was performed under a pressure of about 0.15 baror less at a temperature of 150° C.

The time taken to filter 100 g of the PPS slurry produced by repeatingthe above process was 0.3 hour including additional time for adding,etc., and a total amount of the PPS particles separated and purified wasabout 15.2 g. PPS fine powders remaining in the wastewater afterrecovery were further recovered using a fine filter, and the amountrecovered was about 0.31 g. Accordingly, it was confirmed that arecovery yield of the PPS particles separated and purified with respectto a total amount of the PPS particles recovered was about 98%. Inaddition, it was confirmed that NMP content in washing water collectedthrough the water-washing process performed before the last drying stepwas 500 ppm (0.05 wt %).

Comparative Example 1

The separation and purification process of a polyarylene sulfide wasperformed in the same manner as in Example 1, except that a PPS wet cakewas obtained by performing filtration at room temperature and normalpressure using a vibrating mesh (see FIG. 4) instead of the decantercentrifugal separator shown in FIG. 3 and washed with water without aseparate first drying process, in performing the separation andpurification process of the mixed solution obtained by aliquoting 100 gof the slurry produced in step 1-1 of Example 1 and washing once using50 g of NMP.

The time taken to filter 100 g of the PPS slurry produced by repeatingthe above process was 0.5 hour. A total amount of the PPS particlesseparated and purified was 14.7 g and a recovery yield was about 94.8%.In addition, NMP content in washing water collected through thewater-washing process performed before the last drying step was 4 wt %,from which it can be seen that separation efficiency was greatlyreduced.

Comparative Example 2

The separation and purification process of a polyarylene sulfide wasperformed in the same manner as in Example 1, except that the dryingprocess was performed on a tray at 90° C. under normal pressure insteadof vacuum drying, in performing the separation and purification processof the mixed solution obtained by aliquoting 100 g of the slurryproduced in step 1-1 of Example 1 and washing once using 50 g of NMP.

The time taken to filter 100 g of the PPS slurry produced by repeatingthe above process was 0.3 hour including additional time for adding,etc., and a total amount of the PPS particles separated and purified wasabout 15.4 g. PPS fine powders remaining in the wastewater afterrecovery were further recovered using a fine filter, and the amountrecovered was about 0.11 g. Accordingly, it was confirmed that arecovery yield of the PPS particles separated and purified with respectto a total amount of the PPS particles recovered was about 98%. Inaddition, it was confirmed that NMP content in washing water collectedthrough the water-washing process performed before the last drying stepwas 4000 ppm (0.4 wt %).

1. A separation and purification method of a polyarylene sulfide, comprising: separating polyarylene sulfide particles by sedimentation, and then removing alkali metal halide particles with an organic solvent by sedimentation from a mixed solution containing polyarylene sulfide particles, alkali metal halide particles and an organic solvent by using a decanter centrifugal separator at 1000 rpm to 2500 rpm; and drying the separated polyarylene sulfide particles at 100° C. to 200° C. before washing with water.
 2. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the mixed solution is a waste liquid produced in a synthesizing or washing process of a polyarylene sulfide.
 3. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the polyarylene sulfide particles have a particle size of 100 micrometers to 2000 micrometers.
 4. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the polyarylene sulfide particles have a density of 1 g/cm³ to 1.5 g/cm³.
 5. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the alkali metal halide particles are at least one selected from the group consisting of sodium chloride and sodium iodide.
 6. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the alkali metal halide particles have a particle size of 5 micrometers to 30 micrometers.
 7. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the alkali metal halide particles have a density of 1.9 g/cm³ to 3 g/cm³.
 8. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the organic solvent is at least one selected from the group consisting of N-methyl-2-pyrrolidone, acetone, and isopropyl alcohol.
 9. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the mixed solution further comprises at least one selected from the group consisting of sodium hydroxide, sodium acetate, sodium sulfide, sodium hydrosulfide, and p-dichlorobenzene.
 10. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the drying step is performed under normal pressure or reduced pressure.
 11. The separation and purification method of a polyarylene sulfide according to claim 1, wherein the polyarylene sulfide particles obtained after the drying have a residual amount of the organic solvent of 0.5 wt % or less.
 12. The separation and purification method of a polyarylene sulfide according to claim 1, further comprising washing the polyarylene sulfide particles obtained after the drying with water, followed by drying at 100° C. to 200° C.
 13. A preparation method of a polyarylene sulfide, comprising the preparing a sulfur source comprising a sulfide of an alkali metal and a mixed solvent of water and an amide-based compound by dehydrating a hydrosulfide of an alkali metal and a hydroxide of an alkali metal in a mixed solvent of water and an amide-based compound; preparing polyarylene sulfide particles together with alkali metal halide particles by adding a dihalogenated aromatic compound and an amide-based compound to a reactor containing the sulfur source, and performing a polymerization reaction; washing the polymerization product containing the polyarylene sulfide particles and the alkali metal halide particles with an organic solvent; separating the polyarylene sulfide particles by sedimentation, and then removing the alkali metal halide particles with the organic solvent by sedimentation from a mixed solution containing the polyarylene sulfide particles, the alkali metal halide particles and the organic solvent by using a decanter centrifugal separator at 1000 rpm to 2500 rpm; and drying the separated polyarylene sulfide particles at 100° C. to 200° C. before washing with water. 